1. Field of the Invention
This invention relates to measurement display and control of UFR (Ultrafiltration in Dialysis).
2. Description of the Prior Art
Special reference is made to U.S. Pat. No. 4,486,303, Dec. 4, 1984 as explaining some of the modes of measurement of ultrafiltration in hemodialysis, which is now a well-advanced procedure, depended upon by those who have diseased kidneys. The dialyzer is often referred to as an artificial kidney and saves many lives. However, in certain cases, there are hypotensive episodes due to too little or too much fluid removal. Patient tolerance, or lack of it, to fluid removal is an important factor, but often the dialyzer itself is a contributing factor. The hydraulic permeability is variable.
The current state-of-the-art (with most dialysate delivery systems) does not allow direct control of the rate of ultrafiltration but necessitates the control of transmembrane pressures to control ultrafiltration. The variability of hydraulic permeability can therefore result in variable and unpredictable ultrafiltration. In many dialysate delivery systems, only one pressure is measured on the dialysate side (dialyzer inlet or outlet pressure) and calculations of transmembrane pressure are based on this measured pressure rather than on the mean of the inlet and outlet pressures. As dialysate compartment pressure drops are small, this is normally not a source of large error. However, with some dialyzer designs, poor degassing of the dialysate results in high and variable dialysate compartment pressure drops. This is a consequence of "air locking" of dialysate flow passages. In such situations, ultrafiltration may be erratic and poorly controlled. In some dialyzer designs, the dialysate side pressure drop is a function of the transmembrane pressue because of membrane compliance with consequent changes in dialysate flow geometry. Erratic and unpredictable ultrafiltration may result with such dialyzers.